Various processes have been developed for freezing seafood to maintain the quality of the seafood from the time it is harvested until the time it is prepared for eating. In particular, processes have been developed for rapidly freezing large volumes of fish fillets to retain the product freshness until further processing and cooking by prepared food manufacturers or restaurants.
The most preferred conventional process for producing high quality frozen fillets involves individual quick freezing of the fillets. Fillets are placed on a conveyor that goes through a blast freezer or freezing tunnel to freeze each fillet individually and separate from the other fillets. The fillets are then individually glazed with water or a sugar water solution to inhibit dehydration, and placed in cold storage. Because of the individual processing, the fillets retain their shape and are not subject to breakage. Further, the fillets may later be individually thawed on an as-needed basis by purchasers of the fillets. However, a drawback of this method is the expense and processing limitations associated with individually handling the fillets. Additionally, individually frozen fillets must be stored loosely due to their irregular shapes, with significant voids existing between the fillets. Since much fish processing and freezing is done on board ships, the storage required for the individually frozen fillets is a significant limiting factor. As the frozen fillets are not individually supported in storage, they are subject to breakage and curling.
Several conventional processes have thus been developed for batch-wise freezing of fillets in paperboard cartons. In each of these processes, the cartons are placed in metal pans and slid between horizontal plates, or shelves, of large capacity plate freezers. The shelves are then drawn together to compress and compact the fillets within the cartons, as constrained by the metal pans. The compacted fish fillets are then frozen within the carton by means of refrigerant circulated through the shelves.
The most inexpensive batch-wise, plate freezing method involves filling the paperboard carton with fillets placed randomly therein. During compaction prior to freezing, the fillets are deformed and slide relative to each other within the box to fill any significant air pockets between the fillets. The result of this process is a frozen block in which the fillets are closely intermingled and frozen to each other. Individual fillets cannot be separated from the frozen block without thawing the block, which can result in partial spoilage of the fish near the outer surface of the block prior to thawing of the fish within the interior of the block. It is also difficult to remove the fillets, once thawed, from the block without breakage into smaller pieces. Thus, most often the frozen block is instead sawed into strips or smaller block forms that are then coated with a breeding and fried, since it is not as important to retain the original shape of the fillet for such preparation methods.
An improved batch-wise, plate freezing method has been developed, wherein the fish are frozen in convoluted layers within a carton. This process, commonly referred to as "shatter pack," involves the placement of layers of fish fillets within a carton between sheets of plastic film prior to freezing. Separate sheets of film may be placed between the layers, or alternately a single elongated strip of film can be positioned in an alternating fashion into the box with intermediate layers of fish interposed between. The method is extremely cumbersome due to difficulty in controlling the plastic film during filling the carton. The plastic film is extremely flimsy, and tends to stick to the wet fillets, itself, the processors' hands and equipment, making proper placement of the film difficult.
After freezing in this manner, the layers of fillets can be separated by impacting or jarring the block on a hard surface, shattering the frozen bond lines between the convoluted layers along the plastic film. This method represents an improvement over block frozen fillets, in that it is possible to remove a layer of fillets without thawing the entire block. However, air is introduced between the remaining shattered apart layers, resulting in partial dehydration of the fish during subsequent storage after shattering. Additionally, individual fillets within each layer slide and move over each other during compaction of the layers in the plate freezer. The individual fillets thus contact and overlap each other, and the frozen bonds formed between individual fillets are often stronger than the fillets themselves. Thus during jarring the shatter-packed carton and subsequent attempts to separate the fillets within a layer, many fillets are often broken. Additionally, the plastic film is difficult to remove from crevices formed between the fillets, and must be picked out during cooking of the fillets.
A still further variation on the plate freezing involves the formation of elongated "logs" of fillets by placing fillets in a row on an elongated strip of plastic. The fillets and plastic are then rolled into a solid log, and a plurality of logs are placed parallel to each other in a row within the carton prior to compaction and freezing. The tubular logs are compressed and deformed during freezing, resulting in intimate bonding of the individual fillets within each log to each other. The product produced by this process is typically used for preparing fish sticks, which can be cut or extruded out of individual logs. Otherwise, the entire frozen log must be thawed to remove individual fillets due to the intimate bonding of the fillets within each log.